handle style is None in debugging output

Author: jnothman

pandas/io/excel.py

@@ -1584,7 +1584,7 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
             else:
                 style = self._convert_to_style(cell.style, num_format_str)
                 style_dict[stylekey] = style
-                print(cell.row, cell.col, cell.style, style.__dict__)
+                print(cell.row, cell.col, cell.style, style.__dict__ if style is not None else style)
 
             if cell.mergestart is not None and cell.mergeend is not None:
                 wks.merge_range(startrow + cell.row,